Mass Spectrometry in Inorganic Chemistry - ACS Publications

19 Mass Spectrometric Studies of Scandium, Yttrium, Lanthanum, and Rare-Earth Fluorides

Downloaded by UNIV OF BATH on May 12, 2014 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch019

K. F. ZMBOV and J. L. MARGRAVE Rice University, Houston, Tex.

A review

is presented

of the sublimation -earthtrifluorides.

of recent mass spectrometric

and vaporization

processes

The rates of sublimation

studies

for the

of the

have been measured,

and the heats of sublimation

determined.

Mono-

and difluorides

be produced

in the vapor phase either by vaporizing

fluorides

under reducing

conditions,

or by oxidizing Ionization

for rare-earth

atoms, mono- and difluorides

ured

electron-impact

by

the

involving

method.

the atoms, subfluorides and other thermodynamic

may the

the

trirare-

potentials

have been measGaseous

and trifluorides

ous metals have been studied and used to establish strengths

have been

of the rare-earths

-earth metals with a fluorinating agent.

rare-

trifluorides

equilibria of the

vari-

the

bond

properties.

" D are-earth trifluorides h a v e b e e n p r e p a r e d i n h i g h p u r i t y for use i n A

^

the p r o d u c t i o n of p u r e r a r e - e a r t h metals a n d for v a r i o u s o p t i c a l

a p p l i c a t i o n s , b u t u n t i l r e c e n t l y there h a v e b e e n no q u a n t i t a t i v e d a t a o n t h e i r s u b l i m a t i o n a n d v a p o r i z a t i o n rates. T h e t h e r m o d y n a m i c stabilities of these c o m p o u n d s h a v e also b e e n p o o r l y k n o w n . T h e r e has b e e n some spectroscopic

e v i d e n c e c o n c e r n i n g the monofluorides of Se, Y , a n d L a ,

a n d attempts h a v e b e e n m a d e to c a l c u l a t e d i s s o c i a t i o n energies b y a n a l y z i n g the s p e c t r a l d a t a . T h e u n c e r t a i n t i e s , h o w e v e r , w e r e as h i g h as 1.5 e.v. (2, 3, 7,12,14,

22, 30,

34).

S i n c e the e l e c t r o n i c configurations of the n e u t r a l r a r e - e a r t h atoms differ o n l y i n the 4 / - l e v e l , one m i g h t expect that v a p o r i z a t i o n p r o p e r t i e s , b i n d i n g energies, etc. for the r a r e - e a r t h metals a n d t h e i r

compounds

w o u l d b e essentially i d e n t i c a l , b u t this is f a r f r o m the a c t u a l s i t u a t i o n . H e a t s of v a p o r i z a t i o n of the r a r e - e a r t h metals s h o w a d o u b l e p e r i o d i c i t y 267

In Mass Spectrometry in Inorganic Chemistry; Margrave, J.; Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

268

MASS S P E C T R O M E T R Y

IN INORGANIC C H E M I S T R Y

w i t h i n c r e a s i n g a t o m i c n u m b e r (13, 32, 3 5 ) a n d a s i m i l a r b e h a v i o r w a s f o u n d f o r the d i s s o c i a t i o n energies of r a r e - e a r t h m o n o x i d e s (36).

It has

b e e n s h o w n that there is a p p r e c i a b l e v a r i a t i o n i n the heats of f o r m a t i o n o f t h e s o l i d sesquioxides (15,

16).

O n the other h a n d , r e c e n t m e a s u r e -

ments of the heats of f o r m a t i o n of some rare earth fluorides (28, 29)

indi-

cate o n l y s m a l l differences. T h i s p a p e r presents the results of a n extensive mass s p e c t r o m e t r i c s t u d y of the s u b l i m a t i o n rates for s o l i d r a r e - e a r t h trifluorides a n d of the stabilities of the v a r i o u s gaseous

fluoride

species w h i c h are present i n


equilibrium. Experimental Materials. A l l of the c h e m i c a l s u s e d i n this s t u d y w e r e p u r c h a s e d f r o m S e m i - E l e m e n t s , Inc., S a x o n b u r g , P a . a n d w e r e u s e d w i t h o u t f u r t h e r purification. Mass Spectrometer. T h e mass spectrometer u s e d for analysis of the v a p o r s effusing f r o m the K n u d s e n c e l l w a s a s i n g l e - f o c u s i n g , 1 2 - i n c h r a d i u s of c u r v a t u r e , 60-degree i n s t r u m e n t , e q u i p p e d w i t h a K n u d s e n c e l l assembly. T h e b a s i c features a n d p r i n c i p l e s of o p e r a t i o n of the a p p a r a t u s have been described i n several publications (17). T h e h i g h t e m p e r a t u r e a s s e m b l y consisted of a c y l i n d r i c a l K n u d s e n c e l l , r a d i a t i o n s h i e l d s , a n d a shutter p l a t e . T h e K n u d s e n c e l l w a s m a d e o f t a n t a l u m a n d h a d a r a t i o o f e v a p o r a t i o n surface-to-orifice area o f a b o u t 200. T h e c e l l w a s h e a t e d b y e l e c t r o n b o m b a r d m e n t , a n d the t e m p e r a t u r e w a s m e a s u r e d w i t h a d i s a p p e a r i n g filament o p t i c a l p y r o m e t e r s i g h t e d i n t o a b l a c k - b o d y h o l e t h r o u g h a c a l i b r a t e d flat q u a r t z w i n d o w . T h e optical pyrometer was calibrated b y intercomparison w i t h a similar p y r o m e t e r w h i c h h a d b e e n c a l i b r a t e d b y the U . S. N a t i o n a l B u r e a u of Standards (25). T h e m o l e c u l e s effusing f r o m the K n u d s e n c e l l passed t h r o u g h the slit i n the s h u t t e r p l a t e a n d e n t e r e d the i o n i z a t i o n c h a m b e r of the i o n source, w h e r e the n e u t r a l m o l e c u l e s w e r e i o n i z e d b y electrons. Ions f o r m e d w e r e t h e n a c c e l e r a t e d a n d c o l l i m a t e d b y the i o n lenses i n the i o n source, m a g n e t i c a l l y a n a l y z e d , a n d c o l l e c t e d a n d a m p l i f i e d b y a 16-stage A g - M g d y n o d e e l e c t r o n m u l t i p l i e r w h o s e o u t p u t l e d to a C a r y - v i b r a t i n g r e e d electrometer a n d a L e e d s a n d N o r t h r u p p e n - r e c o r d e r . T h e i n s t r u m e n t w a s also e q u i p p e d w i t h a m o v a b l e p l a t e i n f r o n t of the first d y n o d e of the e l e c t r o n m u l t i p l i e r , a n d this p l a t e c o u l d b e u s e d f o r m e a s u r e m e n t of t h e m u l t i p l i e r g a i n . Results Sublimation Rates of Rare E a r t h Trifluorides. T h e mass s p e c t r a of t h e v a p o r s o v e r s o l i d r a r e - e a r t h trifluorides w e r e s i m p l e . T h e o n l y peaks o b s e r v e d i n t h e r a n g e of t e m p e r a t u r e s i n v e s t i g a t e d w e r e those s p o n d i n g to M , M F , a n d M F +

+

2

+

ions. T h e i n t e n s i t y of M F

v e r y s m a l l , a n d n o p o l y m e r i c species w e r e detected.

3

+

corre-

ions w a s

I o n i z a t i o n efficiency


19.

ZMBov A N D M A R G R A V E

Rare-Earth

269

Fluorides HoF


s

ELECTRON VOLTS (CORRECTED)

Figure 1.

Ionization-efficiency

curves for ions from

HoF -vapors 3

curves for the v a r i o u s ions w e r e m e a s u r e d . F i g u r e 1 shows curves f o r t h e ions f r o m H o F - v a p o r as a t y p i c a l e x a m p l e of a l l the r a r e - e a r t h 3

fluorides.

T h e a p p e a r a n c e potentials of the ions w e r e m e a s u r e d b y the v a n i s h i n g c u r r e n t m e t h o d , u s i n g the i o n i z a t i o n p o t e n t i a l of m e r c u r y , 10.43 e.v. (11)

as a s t a n d a r d to c a l i b r a t e the e l e c t r o n e n e r g y scale. T h e d a t a are

listed i n T a b l e I. B o t h the shapes of the ionization-efficiency curves a n d the values of the a p p e a r a n c e potentials s e r v e d as a basis for c o n c l u d i n g that the ions o b s e r v e d w e r e f o r m e d b y d i s s o c i a t i v e i o n i z a t i o n of M F

3

molecules.

A

v e r y h i g h p r o b a b i l i t y of i o n f o r m a t i o n b y dissociative i o n i z a t i o n c o m p a r e d w i t h s i m p l e i o n i z a t i o n of the p a r e n t m o l e c u l e is c h a r a c t e r i s t i c i n this case as w e l l as i n m a n y other m e t a l h a l i d e systems (4, 10, 2 6 ) . A f t e r the i d e n t i t y of the v a p o r species w a s e s t a b l i s h e d , the s u b l i m a t i o n rates of the trifluorides w e r e d e t e r m i n e d b y f o l l o w i n g the t e m p e r a t u r e d e p e n d e n c e of the M F - i o n i n t e n s i t y at a fixed e n e r g y of i o n i z i n g 2

electrons.

+

T h e d a t a w e r e p l o t t e d as l o g ( Γ Τ )

intensity i n a r b i t r a r y u n i t s , Τ =

vs. 1/T, w h e r e Γ =

ion

t e m p e r a t u r e i n °K. a n d the q u a n t i t y

( Γ Γ ) is p r o p o r t i o n a l to the absolute pressure, P , of the v a p o r (8).


The

270



heats of s u b l i m a t i o n w e r e d e t e r m i n e d f r o m the C l a u s i u s - C l a p e y r o n r e l a tion: d\n(VT) d(l/T)

__AH\

TT

~

R

{

'

O n e c a n also, i n p r i n c i p l e , d e t e r m i n e the heats of s u b l i m a t i o n f r o m the t h i r d - l a w since AF°

ST

W h e r e AF°

T

=

—RT In P

T

a n d AS°

= AH°

-

8>T

(2)

TAS°

8)T

are the changes i n the free e n e r g y a n d t h e

T

e n t r o p y f o r t h e s u b l i m a t i o n process.

This procedure requires that the


a b s o l u t e entropies of the s o l i d a n d gaseous species b e k n o w n . N e i t h e r l o w t e m p e r a t u r e n o r h i g h t e m p e r a t u r e h e a t c a p a c i t y d a t a are a v a i l a b l e for the s o l i d t r i f l u o r i d e s , a n d there are also no s p e c t r o s c o p i c

d a t a or

m o l e c u l a r structures k n o w n to p r o v i d e the necessary i n f o r m a t i o n f o r c a l c u l a t i o n of the e n t r o p i e s ; t h u s , t h i r d - l a w c a l c u l a t i o n s w e r e not m a d e f o r these m a t e r i a l s . Table I.

Appearance Potentials of Ions from R a r e - E a r t h Trifluoride Vapors Appearance

Element

M

Sc Y La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

28.0 28.0 26.5 28.0 27.5 25.5 26.0 27.0 26.5 27.0 27.4 28.0 27.5 27.0 27.0 28.0

+

Potentials MF +

a

MF

16.0 21.5 18.5 20.5 19.0 19.8 19.0 19.5 20.0 19.5 20.0 21.0 20.0 20.8 20.5 21.0

Referred to the ionization potential of H g , LP. = of ± 0 . 7 e.v. a

(e.v.)

10.43 e.v. (11),

+

2

13.5 13.5 12.0 13.0 12.5 12.9 13.0 13.5 14.5 13.0 13.5 14.5 14.0 13.5 14.0 14.3 with an accuracy

T h o u g h s e c o n d - l a w a p p r o a c h e s , as u s e d i n this w o r k for c a l c u l a t i o n of t h e heats of s u b l i m a t i o n , r e q u i r e o n l y a k n o w l e d g e of the r e l a t i v e Γ Γ v a l u e s , the a b s o l u t e pressures of s e v e r a l t r i f l u o r i d e s h a v e b e e n m e a s u r e d b y e v a p o r a t i n g a w e i g h e d a m o u n t of a w e l l outgassed s a m p l e at a c o n stant t e m p e r a t u r e f r o m t h e K n u d s e n c e l l a n d m o n i t o r i n g the

MF


2

+

-ion

19.

zMBov A N D M A R G R A V E

Rare-Earth

p e a k o n the mass spectrometer.

271

Fluorides

F r o m the m e a s u r e d w e i g h t loss, Am, i n

g r a m s , the e v a p o r a t i o n t i m e , t, i n seconds, the t e m p e r a t u r e Τ i n °K., a n d the orifice area, s, i n sq. c m . , one m a y evaluate the absolute v a p o r p r e s sure, P, i n a t m . , f r o m the K n u d s e n - H e r t z e q u a t i o n

44.331 \ s t )

(23).

\MJ

T h e absolute pressures thus o b t a i n e d w e r e u s e d to c a l c u l a t e the m a c h i n e - s e n s i t i v i t y constants r e l a t i n g the pressures a n d i o n currents a n d thus, to y i e l d absolute v a p o r pressure equations. curves for S c F , Y F , a n d L a F Downloaded by UNIV OF BATH on May 12, 2014 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch019

3

-4.0,

3

,

,

,

T h e vapor

pressure

( 2 0 ) are s h o w n i n F i g u r e 2.

3

,

,

,

,

,

π—,

-4.5

ίο / τ (·κ-') 4

Figure 2.

The Vapor Pressure Curves for ScF , YF , and haF 3

:i

Λ

F i g u r e 3 shows the v a p o r pressure c u r v e of N d F , a n d F i g u r e 4 p r e 3

sents the curves for Y b F

3

and L u F .

I n F i g u r e 5 s e c o n d - l a w plots are

3

p r e s e n t e d for the s u b l i m a t i o n o f S m F , P r F , G d F , T b F , a n d T m F . 3

3

3

3

3

F r o m the slopes of these s e c o n d - l a w plots one obtains the heats of s u b l i m a t i o n at the average t e m p e r a t u r e of the measurements. T h e c o r r e c t ions to

ΔΗ°298

cal. deg."

1

w e r e m a d e b y e m p l o y i n g the e s t i m a t e d v a l u e s , ACp =

m o l e " , for the s u b l i m a t i o n process. 1

—7

T h e heats a n d entropies

of s u b l i m a t i o n for the r a r e - e a r t h trifluorides are s u m m a r i z e d i n T a b l e I I . T h e u s u a l u n c e r t a i n t i e s i n the e x p e r i m e n t a l d e t e r m i n a t i o n s of the heats of s u b l i m a t i o n , o b t a i n e d as s t a n d a r d d e v i a t i o n s f r o m a least-squares treatment of the d a t a w e r e of the o r d e r of ± uncertainty ±

5 kcal. mole"

1

1 kcal. mole" . T h e larger 1

at 2 9 8 ° K . i n T a b l e I I reflects b o t h possible


272

M A S S S P E C T R O M E T R Y IN INORGANIC C H E M I S T R Y

errors c a u s e d b y t e m p e r a t u r e gradients i n the c r u c i b l e a n d errors i n the e s t i m a t i o n o f the t h e r m o d y n a m i c q u a n t i t i e s . S t a b i l i t i e s o f R a r e - E a r t h S u b f l u o r i d e s . A l t h o u g h the t r i p o s i t i v e state is the most c o m m o n v a l e n c e state i n the r a r e - e a r t h series, the existence of difluorides of S m , E u , a n d Y b has l o n g b e e n r e c o g n i z e d . T h e r e is also some s p e c t r o s c o p i c e v i d e n c e f o r the existence of the monofluorides of Sc, Y , a n d L a ( 2 , 3, 7 , 1 2 , 1 4 , 22, 30, 34). fluorides

I t has b e e n f o u n d t h a t m a n y s u b -

of the t r a n s i t i o n metals c a n b e i d e n t i f i e d , i n the v a p o r

phase

u n d e r r e d u c i n g c o n d i t i o n s b y mass s p e c t r o m e t r y . I n this w o r k a n a t t e m p t w a s m a d e to p r o d u c e the v a r i o u s subfluorides of the rare-earths a n d to s t u d y

fluorine-exchange

reactions to d e t e r m i n e


the b o n d strengths. T h e r a r e - e a r t h subfluorides w e r e p r o d u c e d b y heat i n g a p p r o p r i a t e m i x t u r e s of r a r e - e a r t h trifluorides w i t h a r e d u c i n g m e t a l , or r a r e - e a r t h metals w i t h a fluorinating agent i n a t a n t a l u m K n u d s e n c e l l . I n the first e x p e r i m e n t of this series, the system N d + studied (37).

BaF

2

was

W i t h the effusion c e l l at t e m p e r a t u r e s b e t w e e n 1330° a n d

1470°K., the i o n species s h o w i n g a c l e a r shutter effect w e r e B a , B a F , +

N d , N d F , and N d F +

+

2

+

.

T h e i o n i z a t i o n efliciency curves for these ions

are s h o w n o n F i g u r e 6.

-4.2

cn UJ or Q. CO

-4.4

\

-4.6

ο Η

1x1 OC

-4.8

3 CO CO UJ

-5.0

CL

-5.2

e> ο _l

•5.4

6.5

6.6

6.7

6.8

6J9

7.0

7.2

71

I0 / ( K ) 4

e

T

Journal of Chemical Physics

Figure 3.

+

The Vapor Pressure Curve for

NdF

3


7.3

ZMBOV AND MARGRAVE


19.

Rare-Earth

273

Fluorides

10 V Τ ( Κ-') β

Journal of Less-Common Metals

Figure 4.

The Vapor Pressure Curves for YbF

3

T h e a p p e a r a n c e p o t e n t i a l of N d - i o n , 5.6 ± +

and

t a i l , w i t h the onset at 5.0 ±

3

0.3 e.v., agrees w e l l w i t h

the v a l u e o b t a i n e d b y the surface i o n i z a t i o n m e t h o d (18) the presence of N d - a t o m s i n the v a p o r . T h e N d F

LuF

+

a n d indicates

c u r v e has a l o w e n e r g y

0.5 e.v. a n d a b r e a k at = N d F

+

+ 2e



274


Figure 5.

Clausius-Clapeyron TbF and TmF +

3

Table II.


Plots for the Variation of SmF \ PrF , Ion Intensities with Temperature 3

+

3

+

3

GdF ,

Heats of Sublimation of Rare-Earth Trifluorides

Temp. Range ΔΗ%,

Δ Η ° s,298

Element

(°K.)

ScF

1172-1323

88.7

101 ± 5

43.2 ± 1.5

1256-1434

100.0

115 ± 5

44.7 ± 1.0

1303-1416

91.7

108 ± 5

37.5 ± 0.7

1301-1485 1327-1491

91.2

99 ± 3 101 ± 5

(38 ± 2) (38 ± 2)

3

YF LaF

3

CeF

3

3

PrF

3

NdF

Τ

92.9

3

1383-1520

85.7

95 ± 5

36.7 ± 0.8

3

1362-1506

96.8

107 ± 5

(45 ± 2) (43 ± 2)

SmF

1382-1522

92.0

100 ± 5

GdF

3

1391-1527

90.3

TbF

3

992-1167

101.7

98 ± 5 111 ± 5

DyF

3

1002-1170

HoF

3

1023-1180

107.5 106.8

1374-1521

EuF

ErF

3

3

TmF YbF

3

1273-1415 1293-1428

LuF

3

1287-1450

3

(41 ± 2) (47 ± 2) 49.4 ± 1.1

111.5

115 ± 5 116 ± 5 120 ± 5

51.9 ± 1.5

89.6

99 ± 5

37.7 ± 0.2

85.5 96.1

95 ± 5

35.5 ± 1.0

103 ± 5

43.1 ± 0.4

49.8 ± 1.1


+

3

19.

ΖΜΒον A N D M A R G R A V E

Rare-Earth

275

Fluorides

.while the b r e a k at 12.5 e.v. corresponds to the f o r m a t i o n of N d F M o n s b y dissociative i o n i z a t i o n of N d F - m o l e c u l e s . T h e N d F - c u r v e begins 2

at 5:6 ±

2

0.5 e.v., a n d has a b r e a k at 13.5 db 0.6 e.v.

agrees w i t h the a p p e a r a n c e p o t e n t i a l of N d F

2

+

+

T h e latter v a l u e

from N d F

found i n the

3

s u b l i m a t i o n studies, w h i l e it w a s a s s u m e d that N d F ( g ) was the n e u t r a l 2

p r e c u r s o r f o r N d F - i o n s at l o w e r e l e c t r o n energies. 2

The

+

appearance

p o t e n t i a l curves for b a r i u m - c o n t a i n i n g ions w e r e s i m i l a r to those r e p o r t e d p r e v i o u s l y f o r the B a F - A l system

(9).

2

T h e a p p e a r a n c e p o t e n t i a l a n d i o n i z a t i o n efficiency

measurements

h a v e e s t a b l i s h e d the presence of B a , B a F , N d , N d F , N d F , a n d 2

NdF

3

m o l e c u l e s i n the gas phase over a B a F - N d m i x t u r e . T h e r e l a t i v e i n t e n s i 2


ties for B a - a n d N d - c o n t a i n i n g ions w e r e m e a s u r e d at v a r i o u s t e m p e r a tures, u s i n g l o w e n e r g y electrons, w i t h voltages — thresholds.

5 e.v. a b o v e the

T h e p o r t i o n of N d F - i o n c u r r e n t c o r r e s p o n d i n g to 2

+

NdF

3

m o l e c u l e s w a s o b t a i n e d f r o m measurements at 18 e.v. a n d b y a p p l y i n g a c o r r e c t i o n for N d F

2

+

f r o m N d F ( g ) , a s s u m i n g a l i n e a r increase of the 2

i n t e n s i t y w i t h the e l e c t r o n energy.

ο

10 4

6

8

10

12

ELECTRON

14

16

VOLTS

18

20

22

24

26

(CORRECTED) Journal of Chemical Physics

Figure 6.

Ionization efficiency curves in Nd-Ba-F

System


28

276

MASS S P E C T R O M E T R Y IN INORGANIC C H E M I S T R Y

T h e i o n intensities w e r e t h e n u s e d to c a l c u l a t e i o n - c u r r e n t analogies of the e q u i l i b r i u m constants for v a r i o u s

fluorine-exchange

e q u i l i b r i a s t u d i e d are l i s t e d i n T a b l e I I I .

reactions.

The

H e r e a g a i n , the c h o i c e of a

m e t h o d for evaluating the reaction enthalpies from the experimental re sults w a s l i m i t e d to the s e c o n d - l a w

procedure

b e c a u s e of the l a c k of

e x p e r i m e n t a l d a t a n e e d e d for c a l c u l a t i n g the t h e r m a l f u n c t i o n s r e q u i r e d i n a t h i r d - l a w treatment. Table III.

Equilibrium Reactions in B a - N d - F System


Reaction Ba(g) + N d F ( g ) = BaF(g) + N d ( g ) (2) 2 B a F ( g ) + N d ( g ) = 2Ba(g) + N d F ( g ) (3) 3 B a F ( g ) + N d ( g ) = 3Ba(g) + NdF (g) (4) B a ( g ) + N d F ( g ) = BaF(g) + NdF(g) (5) 2 B a F ( g ) = B a ( g ) + BaF (s) (6) 3 N d F ( g ) = 2 N d ( g ) + NdF (s) (7) N d F ( g ) + 2 N d ( g ) = 3NdF(g) (8) 2 N d F ( g ) + N d ( g ) = 3NdF (g)

ΔΗ° kcal. mole'

Τ Aug. CK.)

AH° kcal. mole'

1428

- 1 . 9 6 ± 0.85

-4.0 ±

1.0

1428

- 3 . 0 ± 0.9

-4.5 ±

1.2

1428

- 4 3 . 3 ± 5.0

298

T

1

1

(1)

2

3

- 4 6 . 3 ± 5.0

2

2

3

5.8 ±

1.7

8.2 ± 2.0

1428

- 9 1 . 5 ± 3.6

- 1 0 1 . 5 ± 3.6

1455

- 1 2 6 . 6 ± 5.1

- 1 4 2 . 8 ± 5.1

1455

34.0 ± 2.5

43.4 ± 3.0

1455

41.7 ± 2.8

45.2 ± 3.0

1428

3

3

2

T h e plots of l o g K

{

vs. 1/T for the reactions s t u d i e d are p r e s e n t e d

i n F i g u r e s 7, 8, a n d 9. T h e heats of r e a c t i o n o b t a i n e d f r o m the slopes of the curves listed i n T a b l e III.

L i t e r a t u r e d a t a for t h e heat c a p a c i t i e s of

B a F ( g ) , B a F ( g ) , and N d ( g ) 2

(19),

are

Ba(g),

a n d e s t i m a t e d values for N d F ( g ) ,

N d F ( g ) , a n d N d F ( g ) w e r e e m p l o y e d to c a l c u l a t e the e n t h a l p y i n c r e 2

3

ments, ( Η - Η Γ

2 9

8 κ ) . T h e results, c o r r e c t e d to 2 9 8 ° K . , are s h o w n i n the 0

last c o l u m n of T a b l e I I I . B y c o m b i n i n g the heat of R e a c t i o n 1, T a b l e I I I , w i t h the d i s s o c i a t i o n e n e r g y of B a F ( g ) , D tains D °

2 9 8

0

2 9 8

( B a F ) — 134.3 ±

( N d F ) — 130.3 ± 3 k c a l . m o l e "

1

2 kcal. m o l e f

1

one o b

(10)

(5.65 ± 0.13 e . v . ) . U s e of the

same p r o c e d u r e w i t h o t h e r d a t a f r o m T a b l e I I I g i v e A / J t o m [ N d F ( g ) ] 2

a

273.1 =t 5 k c a l . m o l e '

1

and A f f

a t o m

[NdF (g)] 3

Scandium and Y t t r i u m Subfluorides. mining

the stabilities of

heated with C a F

2

— 437.4 ±

—

10 k c a l . m o l e " . 1

I n the e x p e r i m e n t s for deter

S c - a n d Y- subfluorides, these

metals

i n the t a n t a l u m K n u d s e n c e l l . T h e a p p e a r a n c e

were poten

t i a l curves r e v e a l e d the presence of Sc, S c F , S c F , S c F , a n d C a a n d C a F 2

3


ζΜΒον A N D M A R G R A V E

Rare-Earth

277

Fluorides

1.0 1

&

•

·—

0.5

—·

—·

—#

•1 *

0.0

ο

B a ( g H fiJ d F ( g ) = E a F ( g ) f f y d ( g )

3

•

-

- 0 5


•

3BaV(g

-1.0

-1.5 6.5

66

6.7

6.8

6.9

7.0

Î + N d ( g )* 3 B a ( g )

7.1

7.2

= NdF (< ) 3

7.3

7.4

±xl0 ( K ) 4

e

J

Journal of Chemical Physics

Figure 7.

Second-law plots of data for Reactions I., 3, and 4 (Table III)

0.0

Nd£

Mass Spectrometry in Inorganic Chemistry - ACS Publications

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